Abstract: Project III: Gene Therapies for Male Infertility Infertility impacts 10-15% of couples in the United States and a male factor is implicated alone or in combination with female factors in about 50% of cases. Infertility can be caused by hormonal, anatomical, immunological or chromosomal deficiencies, disease or medical treatments, but is frequently of unknown origin (idiopathic). Idiopathic infertility is difficult to counsel and treatment options are empirical. Improved knowledge about the genetic basis of infertility obtained in this program project will aid in the counseling of infertile couples; justify the development of diagnostic screens; and may lead to the development of patient-specific treatment options. Project III will test the hypotheses that: 1) Sertoli cell and germ cell gene therapies can be used to treat nonobstructive azoospermia with maturation arrest (NOA-MA); 2) gene therapy in and around the germline can be achieved with or without germline transmission and 3) germline gene therapy for NOA-MA can eliminate infertility and comorbid somatic diseases from the family lineage. Project I will discover the genetic basis of idiopathic NOA-MA and investigate personal or family histories of overall health problems. Project II will validate genetic variants identified in project I and characterize fertility and overall health comorbidities in mouse models of human NOA-MA. This project will prove the principle that in vivo or ex vivo gene therapies can be used to treat infertility in mouse models of human NOA-MA. For Sertoli cell defects, Aim 1 will prove the principle that in vivo Sertoli cell gene therapy can restore fertility in SCARKO and other mouse models of human NOA-MA with or without germline transmission. For germ cell defects, Aim 2 will prove the principle that ex vivo gene therapy followed by transplantation of spermatogonial stem cells can restore spermatogenesis and fertility in Sohlh1 and Tex11 mouse models of NOA-MA without germline transmission. Aim 3 will test germline gene therapy in Hormad1 and Mcm8 mouse models of human NOA-MA that are associated with overall health comorbidities. We hypothesize that germline gene therapy will restore fertility to the infertile male and reduce or eliminate infertility and associated overall health comorbidities from his family lineage. We will test this hypothesis by collaborating with Project II to examine overall health phenotypes in F1 progeny of gene therapy-treated males. This project will establish the safety and feasibility of gene therapies for male infertility in mouse models to support future translation to the human clinic.